how to get a teenager to go to an expert | ADHD Information

Hi,
I have a diagnosis for ADHS/ADS combined. My son is one of those long running exhausting stories that we keep pulling ourselves up and starting off again with. We are convinced that he also has ADHS/ADS. We have finally found someone who seems quite amazing, we believe she will be able to help my son live a roughly independant life one day as an adult and keep him away from the addictions which he is showing us he has a tendency for. I could have wept with relief when she spoke about things with enormous understanding as if she had been a fly on the wall.
She is a youth psychiatrist and I feel she could help my son. How do we get him there, to her, without destroying him with a load of bad 'you' messages. We want him to feel good about himself and not worse than he does.
We just want some young person out there who has been through this first meeting with the psychi to give us a clue as to how to do it, what to say or what not to say to him. How do we get him in the car. How do we introduce the topic. What shall we say to him? If you have any ideas we will be very grateful.